This invention relates generally to dispersion toughened ceramic composites having increased resistance to fracture, and more particularly to the preparation of such composites by the codeposition of thermal decomposition products which form a matrix of silicon carbide with a dispersed phase of titanium disilicide.
Ceramics are becoming of increasing importance as construction materials for components such as gas turbine blades, pump impellers and the like which are exposed to high temperature environments and/or abrasive or corrosive conditions. Often ceramic materials are toughened to increase resistance to fracture by the addition of a dispersed second phase or fibers such as with the ceramic composites of Al.sub.2 O.sub.3 --ZrO.sub.2, Si.sub.3 N.sub.4 --SiC, Al.sub.2 O.sub.3 --TiC, fiber reinforced silicon carbide, and partially stabilized ZrO.sub.2. The second phase, or dispersed phase, in dispersion toughened ceramic composites is usually provided by the addition of small particles which are randomly dispersed throughout the ceramic matrix. An increase in the toughness of these dispersion hardened ceramic composites occurs when a metastable second phase in the ceramic matrix absorbs energy from the stress field of an advancing crack and transforms this energy to a stable phase in the ceramic as in the case of partially stabilized zirconia. Also, mechanical toughness of the ceramic can be increased when a stable dispersed phase absorbs energy from a stress field causing plastic deformation or crack diversion and branching by the second phase.
The preferred microstructure of a dispersion toughened ceramic composite is provided by dispersing particulates throughout the ceramic matrix. However, such microstructures are not readily provided by employing conventional powder blending and consolidation techniques, primarily due to the fact that the dispersed particles are typically somewhat larger than desired and uniform distribution throughout the matrix is seldom achieved. Also, in covalently bonded compounds such as nitrides and carbides, high densities are often difficult to achieve due to the sintering characteristics of such materials.